Anesthetic apparatus

ABSTRACT

A closed reservoir charged with a supply of liquid anesthetic material communicates via a conduit with a vaporizer chamber through which a stream of gas flows. The reservoir is pressurized by a pressure line communicating with the reservoir at a region beneath the surface of the liquid, and a pressure head is maintained independently of the level of the anesthetic material in the reservoir. The rate of flow of liquid through the conduit to the vaporizer chamber is controlled by regulating the pressure within the pressure line relative to the pressure within the pressure line relative to the pressure within the vaporizer chamber. The reservoir may be formed by an anesthetic containing bottle in sealing engagement with a support for the vaporizer to provide a compact assembly.

United States Patent 2,342,602 2/1944 Reitz, Jr. 128/188 3,128,7644/1964 Koehnm 128/188 3,171,411 3/1965 Levine 128/188 PrimaryExaminerRichard A. Gaudet Assistant Examiner-J B. MitchellAtt0rneyMason, Kolemainen, Rathburn and Wyss ABSTRACT: A closedreservoir charged with a supply of liquid anesthetic materialcommunicates via a conduit with a vaporizer chamber through which astream of gas flows. The reservoir is pressurized by a pressure linecommunicating with the reservoir at a region beneath the surface of theliquid, and a presure head is maintained independently of the level ofthe anesthetic material in the reservoirv The rate of flow of liquidthrough the conduit to the vaporizer chamber is controlled by regulatingthe pressure within the pressure line relative to the pressure withinthe pressure line relative to the pressure within the vaporizer chamber.The reservoir may be formed by an anesthetic containing bottle insealing engagement with a support for the vaporizer to provide a compactassembly.

[72] Inventors Francis J. Elchelman Ll Grange Park; Andrew A. Kenny,Chicago, both 01, Ill. [21 Appl. No. 793,932 [22] Filed Jan. 27, 1969[45] Patented July 20, 1971 [73] Assignee Chemetron Corporation Chicago,111.

[54 ANESTIIETIC APPARATUS 18 Claims, 7 Drawing Figs.

[52] US. Cl 128/188 [51] int. Cl A6lm 17/00 [50] FieldnlSearch 128/188,186,187, 189,204,193-196,197,173,173.1, 251, 1 13, 1 14 [56] ReferencesCited UNITED STATES PATENTS 458.937 9/1891 Blass 48/195 SOURCE OFPRESSURIZED was man: mix was l/ T/L lZ/NG APP/'1 RA TU5 1 SOURCE OFPRESSUR/ZED ANIS'IHE'IIC APPARATUS The present invention relates toanesthetic apparatus, and more particularly to apparatus for introducinganesthetic vapor into a gas stream for use in anesthetizing a patient.

In the process of inducing a state of anesthesia in a patient, thepatient is caused to inhale a mixture of a gas, such as oxygen, and ananesthetic vapor. Several inhalation anesthetic materials are currentlyused, including ether, halothane (available under the trademarkFluothane), trichloroethylene, methoayflurane (available under thetrademark Penthrane) and others. The desired concentration of any givenanesthetic vapor in oxygen or other gas varies in dependence upon theparticular patient, and may vary over a considerable range as anesthesiais first induced and subsequently maintained at a given stage. Inaddition, the range of concentration varies for different materials. Forexample, the concentration of ether in some cases may be as high as 8percent or more, while methoxyllurane may be administered at aconcentration as low as 0.2 percent.

Anesthetic materials are customarily available in the form of volatileliquids, and various methods have been used for evaporating the liquidanesthetic into a gas stream. Anesthetic apparatus known heretofore hasbeen subject to one or more problems, including lack of accuracy inachieving the desired concentration, particularly over the wide range ofconcentrations necessary for use with different anesthetic materials,undue complexity, expense, and inconvenience. One common method is tobubble a stream of gas through a supply of liquid anesthetic to producea highly concentrated mixture. Subsequently the mixture is diluted toachieve the desired concentration. One difficulty encountered with thismethod arises in accurately attaining the desired concentration sincethe rate of evaporation varies widely with temperature and pressureconditions.

Other known methods involve the use of vaporizing apparatus throughwhich a stream of gas is passed. A metered amount of liquid anestheticis introduced into the vaporizing apparatus and evaporates into the gasstream. The accuracy of this arrangement is not highly dependent upontemperature and pressure conditions because all of the liquid anestheticintroduced into the vaporizing apparatus is intended to evaporate intothe gas stream. However, difficulties are encountered in accuratelymetering the amount of liquid anesthetic which is introduced into thevaporizing apparatus, and in maintaining a constant pressure head forforcing the liquid anesthetic into the vaporizing apparatus. One exampleof a system of this type may be found in U.S. Pat. No. 3,128,764 issuedto Wilbur R. Koehn.

Accordingly, it is an object of the present invention to provideimproved anesthetic apparatus for providing a gas and anesthetic mixturewhich can be controlled accurately over a wide range of concentrations.

Another object is to provide improved anesthetic apparatus which issimple and convenient to operate.

A further object is to provide improved apparatus for maintsining a,constant pressure head for evacuating anesthetic liquid from a containerat a rate independent of a changing liquid level.

Another object is to provide an apparatus in which the anestheticconcentration can be varied over a wide range and controlled with greataccuracy.

Another object of the invention is to provide improved anestheticapparatus suitable for use with a wide variety of anesthetic materialsand for use in both closed and open systems.

in brief, anesthetic apparatus constructed in accordance with theinvention may include a vaporizer chamber through which flows a streamof gas to which anesthetic vapor is to be added. An anesthetic materialin the liquid state is introduced into the vaporizer chamber through aconduit from a closed cordance with an important feature of theinvention, pressure within the reservoir forces the anesthetic throughthe conduit to the vaporizer chamber at a rate which is independent ofthe level of anesthetic in the reservoir. Accordingly, there is norequirement to maintain a constant level in the reservoir as in manyprior art systems. In order to accomplish this result, the reservoir ispressurized by means of a pressure line communicating with the reservoirat a region beneath the surface of the anesthetic.

The rate at which liquid flows into the vaporizer chamber is regulatedaccurately and conveniently by varying the pressure differentialexisting between the vaporizer chamber and the reservoir. In accordancewith a feature of the invention, the pressure differential may becontrolled by regulating the pressure of the pressure line communicatingwith the reservoir, or by regulating the pressure within the vaporizerchamber, or both.

Another feature of the invention resides in the simplicity andconvenience of the vaporizer apparatus. In certain embodiments of theinvention, the closed reservoir containing the liquid anestheticcomprises the bottle or container in which the liquid anesthetic issupplied. The bottle is held in sealing relation to a support memberassociated with the vaporizer, and both the pressure line and the liquidconduit extend into the bottle to a point beneath the surface of theliquid anesthetic contained in the bottle. This arrangement, in additionto being extremely simple and inexpensive, reduces the evaporation wasteoccurring with prior art apparatus, and also makes it extremely simpleto change quickly from one anesthetic material to another.

The apparatus of the present invention may also include a novelarrangement for maintaining an even pressure differential between thevaporizer chamber and the regulator by controlling the reservoirpressure in accordance with minor fluctuations within the vaporizerchamber. in addition, a restricted bleed line may extend between thereservoir and the vaporizer chamber to prevent the buildup of excesspressure within the reservoir due to accelerated evaporation of theliquid anesthetic contained therein. A dual-purpose valve with a singlecontrol may be used to control the admission of pressurized gas to theregulator, and also to regulate the gas stream passing through thevaporizer chamber.

The above and many other objects and advantages of the present inventionwill appear from the following detailed description of certainembodiments of the invention taken with the accompanying drawings, inwhich:

FIG. I is a diagrammatic and elevational view, partly in section, ofvaporizer apparatus constructed in accordance with the invention;

FIG. 2 is a diagrammatic and elevational view, partly in section, of analternative embodiment of the invention;

FIG. 3 is a diagrammatic and elevational view, partly in section, ofanother alternative embodiment of the invention;

FIG. 4 is a perspective view of a self-contained vaporizer unitincluding the components illustrated in FIG. 3;

FIG. 5 is an exploded view of the unit of FIG. 4;

FIG. 6 is an enlarged sectional view taken along the line 6-6 of FIG. 4;and

FIG. 7 is an elevational view of one side of the unit of FIG. 4.

Referring now to the drawings, and initially to FIG. I, there isillustrated a liquid anesthetic vaporizing unit generally designated as10 and constructed in accordance with the present invention. In themain, the unit I0 includes a vaporizer chamber designated as a whole bythe reference numeral [2 and a closed reservoir generally designated as14. A stream of gas to which an anesthetic vapor is to be added isconducted from a source of pressurized gas through a shutoff valve ISand through the vaporizer chamber 12 by means of an inlet conduit 16 andan outlet conduit 18 communicating with anesthetic mixture utilizingapparatus which may, for exarnple. be part of a closed or an openanesthetic system. In an reservoir charged with a supply of anestheticliquid. In acopen system a gas, such as oxygen, is passed through thevaporizer chamber 12 and mixed with a desired concentration ofanesthetic vapor, and is forwarded via the outlet conduit 18 to patientbreathing apparatus. In a closed system, the gaseous mixture is recycledthrough a closed circuit in which carbon dioxide is removed from theexhaled gas and additional oxygen combined with anesthetic vapor isadded to replenish the flow.

In accordance with one important feature of the invention, liquidanesthetic is forced to flow from the closed reservoir [4 through aliquid carrying conduit 20 to the vaporizer chamber I2 at a rate whichis accurately controlled and is independent of the liquid level in thereservoir 14. The reservoir 14 is initially charged with a supply ofanesthetic liquid and no effort is made to maintain a constant levelwithin the reservoir [4 as the liquid anesthetic is used. In order toprovide a flow of fluid through the conduit 20 at a rate independent ofthe liquid level in the reservoir 14, the reservoir [4 is pressurized bymeans ofa pressure line 22 having an end 220 communicating with thereservoir preferably near the bottom so as to be beneath the surfaceofliquid in the reservoir. Accordingly, for a given pressure in thepressure line 22, the pressure head causing evacuation of the liquidthrough the conduit 20 remains constant regardless of the level ofliquid in the reservoir l4, and without the necessity for specialcontrol apparatus. This represents a substantial advance in convenienceand simplicity over prior art arrangements wherein com plicated andexpensive apparatus was required to maintain a constant anesthetic levelin order to maintain a constant pressure head for forcing liquid fromthe reservoir into the vaporizer.

More specifically, the pressure head at the lower end 200 of the liquidconduit 20 is made up of two components. One component of the pressurehead is produced by the pressure of the vapor or gas within thereservoir 14 above the surface of the liquid contained therein. Theother pressure component results from the weight of the liquid withinthe reservoir 14 above the lower end 20a of the conduit 20.

In prior art apparatus, attempts have been made to maintain a constantpressure head by maintaining the liquid level in the reservoir constantand by maintaining the pressure of the atmosphere within the reservoirconstant. This approach, however, has required a complicated valvingmechanism for maintaining a constant liquid level. In contrast, thepresent invention provides a simplified, less expensive and convenientlyregulated arrangement for maintaining a constant pressure head at thelower end of the conduit 20.

In the arrangement of the present invention, the liquid level does notremain constant and the component of the pressure head caused by theliquid decreases as the liquid level falls. However, since thiscomponent of the pressure head acts on the submerged pressure line 22 aswell as on the liquid conduit 20, the pressure of the gas containedwithin the reservoir l4 increases and compensates for the falling liquidlevel. Accordingly, the pressure head effective at the end 20a of theconduit 20 remains constant for a given pressure within the pressureline 22.

Although the lower ends 20a and 22a of the liquid conduit 20 andpressure line 22 are illustrated in FIG. I at approximately the samelevel, it will be obvious that they may be disposed at different levelsif desired. A constant effective pressure head will be maintained aslong as both the pressure line and the liquid conduit terminate beneaththe surface of the liquid.

As noted above, the apparatus of the present invention is capable ofproviding accurately controlled anesthetic concentrations over a widerange. The conduit 20 is preferably of capillary size and may include asegment having an inner diameter in the neighborhood of 0.007 inch. Theflow of liquid anesthetic through the conduit 20 is governed by therules of laminar flow, in accordance with which the flow through theconduit 20 is proportional to the pressure differential existing betweenthe lower end 20a of the conduit and an upper end 20b disposed withinthe vaporizer chamber 12. Since the pressure at the lower end 200 of theconduit 20 is determined by the pressure within the pressure line 22,the rate of flow of liquid anesthetic into the vaporizing chamber I2 ispropor tional to the pressure differential existing between the pressureline 22 and the interior of the vaporizer chamber 12.

In accordance with a feature of the invention, the rate of flow ofliquid anesthetic through the conduit 20, and thus the percentageconcentration of anesthetic vapor in the stream of gas, is accuratelycontrolled over a broad range by controlling the pressure within thereservoir 14 relative to the pressure within the vaporizer 12. In theembodiment ofthe invention illustrated in FIG. I this is accomplished bycontrolling the pressure existing within the pressure line 22 by meansof a pressure line regulator generally designated as 24, and controllingthe pressure within the vaporizer chamber 12 by means of a back pressureregulator generally designated as 26.

More specifically, the pressure line 22 communicates with the outlet ofapressure regulated valve 28, the inlet of which is connected to a sourceof pressurized gas by way of a shutoff valve 30. If desired a singlesource may be used both for the gas stream entering the inlet conduit toand for supplying the regulator 24, although separate sources areindicated in FIG. 1. The pressure regulator 24 may be of any suitabletype, and as illustrated includes a diaphragm 32 acted upon by thepressure within the pressure line 22 and coupled to the valve 28 bymeans of a linkage 34 for operating the valve to maintain a constantpressure within the pressure line 22. The pressure acting upon thediaphragm 32 is opposed by the force applied by a spring 36, andpreferably the spring tension is adjustable by means of a handle 38 withwhich the constant pressure level to be maintained within the pressureline 22 may be varied.

The back pressure regulator 26 may be of any desired type, and isillustrated as being similar in many respects to the pressure lineregulator 24. The gaseous mixture flowing from the vaporizer chamber I2passes via the outlet conduit I8 to the inlet of a pressure regulatedvalve 40, the outlet of which is connected to the anesthetic mixtureutilizing apparatus. The valve 40 is controlled by means ofa linkage 42and diaphragm 44 to maintain the pressure at the inlet side of the valve40, and thus the pressure within the vaporizer chamber 12, at a constantlevel. The pressure within the vaporizer chamber I2 is adjusted to adesired level by means of a handle 46 controlling the tension of aspring 48 acting on the diaphragm 44.

Since the rate of flow of liquid anesthetic through the conduit 20 isdetermined by the pressure differential existing between the pressureline 22 and the vaporizer chamber 12, the concentration of theanesthetic in the gas stream can conveniently and accurately be adjustedby means of the handles 38 and 46 of the pressure line regulator and theback pressure regulator. It is possible with the apparatus of thepresent invention to regulate the pressure differential and thus theflow rate with either one of the regulators 24 and 26, the other beingomitted or combined with other equipment. Alternatively, one of theregulators 24 and 26 may be permanently set or factory adjusted at aselected level and the other may be adjusted by the anesthesiologist. Ifdesired, of course, both of the regulators may be used. For example, oneof the regulators may be set at a selected level to give a certain rangeof flow rates, and the other used for finer adjustments within theselected range.

A pair of pressure responsive indicators 50 and 52 are connectedrespectively to the pressure line 22 and the outlet conduit l8communicating with the interior of the vaporizer chamber 12. Thereadings of the indicators 50 and 52 indicate the pressure differentialexisting between the pressure line 22 and the vaporizer chamber 12, andthus the anesthetic concentration may be computed from this pressuredifferential. Alternatively, the indicators 50 and 52 may be providedwith scales (not shown) calibrated in terms of anesthetic concentration.

It will be appreciated that due to factors such as friction and inertiaassociated with the elements of the back pressure regu lator 26, minorpressure variations and fluctuations may exist within the vaporizerchamber 12. Although these variations are of a minor and transientcharacter, it may be desirable to compensate for such variations inorder to provide an evenly regulated flow of liquid from the reservoir14 into the vaporizer chamber 12. In order to accomplish this, apressure equalizing line 53 extends from the interior of the vaporizerchamber 12 to the dome portion of the pressure line regulator 24.Pressure variations existing within the vaporizer chamber l2 arecommunicated via the equalizing line 53 to the reverse or dome side ofthe diaphragm 32 automatically to control the valve 28 for maintaining aconstant pressure differential between the vaporizer chamber and thereservoir.

With some anesthetic material such as ether a problem may arise when thereservoir 14 is exposed to light or temperature variations. Under someconditions it is possible for the liquid within the reservoir 14 toevaporate at an accelerated rate and for the vapor pressure within thereservoir 14 to increase to an undesirable level. Rather thancontrolling the external conditions affecting the rate of evaporation,it may be preferable to provide a restricted bleed line 54 extendingfrom the upper portion of the closed reservoir 14 to the interior of thevaporizer chamber 12. This line has a very small interior diameter, andserves very gradually to vent any excess pressures that may exist withinthe reservoir l4 to the lower pressure region within the vaporizerchamber 12. The line is small in size, and the limited flow of gastherethrough may readily be compensated for through calibration of thesystem.

Referring now to the construction of the vaporizer chamber 12, thechamber includes a cylindrical wall member 56 defining an interiorchamber and preferably fonned of transparent material such as glass inorder to permit viewing of the flow of anesthetic liquid from theconduit 20. The upper end b of the conduit 20 is provided with a dripguide 58 for causing the liquid to form droplets rather than runningdown the outer surface of the conduit 20 and/or into the line 54.

The upper and lower ends of the cylindrical wall 56 are closed by bodymembers 60 and 62. The upper body member 60 includes a pair of passagesI80 and 53a communicating respectively with the outlet conduit 18 andthe pressure equalizing line 53, and communicating with the interior ofthe vaporizer chamber [2. Similarly, the lower body member 62 includes apassageway 16a communicating with the iniet conduit l6 and with theinterior of the vaporizer chamber 12.

The vaporizer chamber I2 is divided into two regions by means of aporous metal diffusion plate or baffle 64 supported within the lowerbody section 62. The stream of gas entering through the inlet conduit 16passes through the diffusion plate 64 to reach the outlet conduit 18.Liquid anesthetic emerging from the conduit 20 falls from the drip guide58 onto the plate 64 and is completely evaporated into the stream of gasmoving through the plate 64.

With the vaporizing unit [0 of the present invention it is not necessaryto transfer the liquid anesthetic from its original container to aseparate reservoir. In addition to being convenient, this arrangementprevents the evaporation loss, contarnination, and the like sufferedwith known equipment during transferral of liquid anesthetic from onevessel to another. Since the liquid is kept in its original container,the possibility of confusion as to what type of anesthetic is being usedis reduced.

In order to permit the original container or bottle 66 in which theanesthetic is obtained to serve as the closed reservoir in the system,the lower body member 62 supports a sealing member 68 having a lowersurface against which the neck of the bottle 66 abuts. The bottle 66 isheld in sealing engagement with the sealing block 68 by means of a yoke70 pivotally supported by the lower body member 62 and a clamping bolt72 engaging the bottom of the bottle 66. Since the pressure line 22 andthe conduit 20 extend downwardly through the lower surface of thesealing block 68. the unit I0 is assembled for operation merely bypositioning the bottle 66 and clamping it in place.

One of the advantages of the apparatus of the present invention is thatit may be used with a high degree of accuracy over a wide range ofanesthetic vapor concentration levels. Accordingly, the apparatus iswell suited for use with a wide variety of different anestheticmaterials which may require concentrations falling in widely varyingranges. However, if for precautionary reasons it is desired to restrictthe use of the unit 10 to one particular anesthetic at one given time asuitable indexing means (not shown) may be provided on the sealingmember 68 so that the unit can accept only one particular type of bottleassociated with the one selected anesthetic material.

Reviewing the operation of the liquid anesthetic vaporizing unit 10,initially there is no stream of gas flowing through the vaporizerchamber 12 and the shutoff valves 15 and 30 are in the off position. inorder to prepare the unit for operation, a bottle 66 of a selectedanesthetic material is mounted against the sealing member 68 and clampedin place by the clamping bolt '12. The valve I5 is opened and the flowof gas through the vaporizer chamber I2 is begun. The shutoff valve 30is opened and one or both of the regulators 24 and 26 are adjusted bymeans of the adjusting handles 38 and 46 to provide a desired pressuredifferential between the lower end 200 and the upper end 20!; of theliquid conduit 20. Pressurized gas from the source of pressurized gasflows through the pressure line regulator 24, where its pressure isdropped to the selected level, and then through the pressure line 22 andinto the closed reservoir 14. Pressure within the reservoir forcesliquid anesthetic material through the conduit 20 to the vaporizerchamber 12 where it drips onto the diffusion plate 64.

Gas entering the vaporizer chamber 12 through the conduit 16 flowsthrough the plate 64 and is mixed with evaporating anesthetic. Thegaseous anesthetic mixture then flows through the outlet conduit 18 andthrough the back pressure regulator 26 to the utilizing apparatus. Theback pressure regulator maintains a selected pressure level within thevaporizer chamber 12. As the liquid level drops in the reservoir 14, thepressure differential between the ends 20a and 20b of the conduit 20, asdetermined by the regulators 24 and 26, does not vary and the rate offlow of anesthetic remains constant.

If it is desired to change anesthetics or replace the bottle 66, theshutoff valve 30 is closed, and the pressure within the reservoir 14drops quickly due to provision of the bleed line 54 to stop the flow ofliquid through the conduit 20. Since the reservoir 14 is located belowthe chamber 12, there is no liquid flow in the absence of pressurewithin the reservoir. in addition, when the bottle 66 is removed theconduit 22 is rapidly purged of liquid by the force of gravity.

ln apparatus constructed in accordance with the present invention it wasfound that the unit could be used with different types of anesthetics,and that the concentration of anesthetic in the gas stream could becontrolled accurately over wide ranges. in addition it was observed thatthe flow of anesthetic remained constant even though the liquid level inthe reservoir decreased due to the novel arrangement for pressurizingthe reservoir with a pressure line terminating beneath the surface oftheliquid.

For example, in one unit constructed in accordance with the invention,the liquid conduit 20 included a capillary size segment one-half inch inlength and 0.0075 inch in diameter. The regulator 24 was adjusted sothat the pressure within the line 22 was the equivalent of 24 inches ofwater. An oxygen gas stream was passed through the vaporizer at a rateof 1,000 cubic centimeters per minute. The reservoir 14 was charged witha supply of liquid ether, and the regulator 26 was adjusted to maintainthe interior of the vaporizer at a pressure equivalent to 15.2 inches ofwater. Liquid ether flowed into the vaporizer at a rate equivalent to 66cubic centimeters of vapor per minute and was evaporated into the gasstream to produce an anesthetic mixture of 6.6 percent ether vapor inoxygen.

The unit was also capable of operation with other anesthetics and atother concentrations. For example, the

reservoir 14 was charged with a supply of liquid halothane and theregulator 26 was adjusted to maintain the interior of the vaporizer 12at a pressure equivalent to l 1.8 inches of water, while the othervariables remained the same as in the previous example. Liquid halothaneflowed into the vaporizer at a rate equivalent to 28 cubic centimetersper minute of vapor, and an anesthetic mixture of 2.8 percent ofhalothane vapor in oxygen was produced as the liquid evaporated into thegas stream.

It should be understood that the above examples are set forth only as anillustration of one embodiment of the invention. The specificinformation included here should not be taken to limit the invention,which is defined in the claims appended to the specification.

Having reference now to FIG. 2, there is illustrated an anestheticvaporizing unit generally designated as 80 and comprising an alternativeembodiment of the present invention. The unit 80 includes a vaporizerchamber designated as a whole as 82 together with a closed reservoirgenerally designated as 84. A stream oigas to which an anesthetic vaporis to be added is conducted from a source of pressurized gas, through ashutoff valve 86 and through a conduit 88 to the vaporizer chamber 82where an anesthetic vapor is added to the gas stream. The anesthetic andgas mixture leaves the vaporizer chamber 82 through a conduit 90 and issupplied to suitable anesthetic mixture utilizing apparatus.

As with the unit illustrated in FIG. I and described above, liquidanesthetic is forced to flow from the closed reservoir 84 into asubmerged lower end 920 of a liquid conduit 92 and to the vaporizerchamber 82 at a rate of flow which is independent of the level of liquidin the reservoir 84. In accordance with the invention, the reservoir 84is pressurized by means of a pressure line 94 having a lower end 940communicating with the reservoir at a region beneath the surface of theanesthetic liquid in normal operation.

Thus, as described in detail in connection with the embodiment of FIG.I, for a given constant pressure in the pressure line 22, the pressurehead causing evacuation of liquid through the liquid conduit 92 remainsconstant regardless of the level of liquid in the reservoir 84.

The embodiment of the invention illustrated in FIG. 2 dif fers from theunit It] described above in that the liquid conduit 92 communicates withthe interior of the vaporizer chamber 82 by way ofa metering valve 96.Valve 96 includes an operat ing handle 98 with which the valve settingmay be varied between several different settings thereby to vary theresistance to the flow of liquid from the reservoir 84 to the vaporizer82. The valve 96 may be of any known type such as a variable orificevalve, or a valve of the type in which movement of the operating handleserves to vary the effective length of a capillary size passageway.

In accordance with a feature of the invention the rate of flow ofanesthetic from the reservoir 84 to the vaporizer 82, and thus theconcentration of the gas anesthetic mixture, is controlled by regulatingthe pressure differential existing between the reservoir 84 and thevaporizer 82 and/or by operating the metering valve 96 to vary theresistance to flow between the reservoir 84 and the vaporizer 82. In thearrangement of FIG. 2, the unit 80 is illustrated as used withanesthetic mixture utilizing apparatus of a type which maintains thepressure within the vaporizer chamber 82 substantially constant,although a back pressure regulator similar to the regulator 26 of FIG. Icould be used if desired. Accordingly, the pressure differential betweenthe reservoir 84 and the vaporizer 82 is varied by controlling thepressure in the pressure line 94 with a pressure line regulatorgenerally designated as I00 and including a pressure regulated valve I02having its inlet connected through a conduit I04 to the shutoff valve86, and having its outlet connected to the pressure line 94. The valveI02 is controlled by a linkage I06 operated by a diaphragm I08 actedupon by the pressure within the pressure line 94 in opposition to aspring III], the tension of which is adjustable by means ofa handle I12.

Since the rate of flow of liquid anesthetic to the conduit 92, for anyparticular setting of the metering valve 96, is proportional to thepressure differential existing between the reservoir 84 and thevaporizer 82, the rate of flow may be adjusted by operation of thehandle I12 to a setting which provides the desired constant pressurewithin the pressure line 94. A pressure responsive indicator [I4communicates with the pressure line 94 to provide a pressure reading or,if desired, a direct reading of the pressure differential existingbetween the reservoir 84 and the vaporizer chamber 82.

Referring now more specifically to the construction of the vaporizerchamber 82, this chamber may be constructed in any suitable fashion andis illustrated as including a trans parent cylindrical wall I16 havingits upper and lower ends closed by body members I18 and I20. The bodymembers are provided with suitable passageways 88a, 90a and 92bcommunicating between the interior of the vaporizer chamber and theconduits 88, 90 and 92 respectively.

In order to evaporate the liquid anesthetic reaching the vaporizerchamber into the flowing gas stream a porous metal diffusion plate orbaffle I22 divides the vaporizer chamber 82 into two regions. The streamof gas entering through the conduit 88 passes through the plate I22 andthrough the conduit 90 to the anesthetic mixture utilizing apparatus.Liquid anesthetic entering the vaporizer chamber 82 from the conduit 92falls onto the plate 122 and is completely evaporated into the gasstream flowing through plate 122.

The liquid reservoir 84 of the unit 80 may be of any desiredconstruction and as illustrated includes a container I24 closed by meansofa sealing member 126 held against the container 124 by a suitableclamp or other means (not shown). It should be appreciated that ifdesired the unit 80 of FIG. 2, may in clude an arrangement such asillustrated in the unit 10 of FIG. I wherein the reservoir comprises theoriginal container of the liquid anesthetic and wherein the reservoirand the vaporizer chamber are combined in a single unit. In addition,the unit 80 may be provided with a restricted bleed conduit and with apressure equalizing line similar to the conduit 54 and line 53 oftheunit illustrated in FIG. I.

In the operation of the unit 80, when it is desired to provide a mixtureof gas and anesthetic the shutoff valve 86 is opened so that a stream ofgas flows through the vaporizer chamber 82 and to the anesthetic mixtureutilizing apparatus. The reservoir 84 is charged with a supply ofanesthetic liquid, and the metering valve 96 as well as the pressureline regulator I00 are adjusted to selected settings for producing thedesired concentration of liquid anesthetic in the gas stream. The liquidanesthetic is evacuated from the reservoir 84 through the liquid conduit92 and into the vaporizer chamber 82 where the liquid evaporatescompletely into the gas stream. The effective pressure head within thereservoir 84 causing the evacuation of the liquid remains constant asthe liquid level falls due to the fact that the reservoir is pressurizedby the pressure line 94 which terminates at a point beneath the surfaceof the liquid.

Having reference now to FIGS. 3-7, there is illustrated a liquidanesthetic vaporizing unit designated as a whole by the referencenumeral and comprising a further embodiment of the present invention. Asbest shown in FIG. 3, wherein the unit I40 is illustrated in somewhatschematic form, the unit in general includes a vaporizer chambergenerally designated as 142 together with a liquid anesthetic reservoirgenerally designated as I44. A stream of gas to which an anestheticvapor is to be added is conducted from a source of pressurized gasthrough a conventional shutoff valve I46 and through a conduit I48 andinto the vaporizer chamber I42. Within the vaporizer chamber, a liquidanesthetic is vaporized and mixed with the stream of gas, and themixture of gas and an anesthetic is conducted to an anesthetic mixtureutilizing apparatus by way of a conduit 150.

As with the units described above in connection with FIGS. 1 and 2, theunit I40 operates to supply a uniform anesthetic concentrationregardless of the level ofliquid anesthetic in the reservoir 144.Furthermore the concentration is accurately controlled and is variableover a wide range. In addition, and in accordance with further featuresofthe invention, the unit is conveniently arranged in a compact packagewith all controls and connections readily accessible. Furthermore asinglemanual control serves to operate a novel dual-purpose valve tocontrol both the admission of pressurized gas to the reservoir and tocontrol the volume of gas flow into the vaporizer through conduit 148.

As best shown in FIGS. 4 and 5, the unit 140 shown schematically in FIG.3 comprises a compact assembly including a housing 152 with thevaporizer chamber I42 and the liquid anesthetic reservoir 144 mounted inan accessible location on the exterior thereof. This construction hasthe advantage that much of the apparatus is safely enclosed within thehousing I52, while the reservoir I44, chamber I42 and the necessarycontrols are readily accessible to an operator.

Proceeding now to a more detailed description of the reservoir I44 andthe vaporizer chamber 142, these elements are best illustrated in FIG.6. The vaporizer chamber comprises a somewhat bell-shaped enclosure I54preferably formed of glass or other transparent material. The enclosureI54 is held in position over a base member 156 by a threaded clamp ring158. The interior of the vaporizer chamber enclosure 154 is sealed by apair of sealing gaskets I60 and 162 held in compression by the clampring 158. The upper portion of the vaporizer enclosure 154 iscommunicated with the conduit 150 by means of a fitting 164 threadedlyconnected to an elbow 166. A pair of seals 168 and I70 are held incompression against the wall of the enclosure 154 by engagement betweenthe fitting I64 and the elbow 166.

In order to admit a stream of gas to the lower portion of the vaporizerchamber from the conduit I48, the base member 156 includes a passageway148a extending from the lower surface of the base member I56 to theinterior of the vaporizer chamber I42. A porous metal diffusion plate orbaffle I72 extends across the vaporizer chamber 142 between thepassageway 148a and the fitting 164 in order to accomplish theevaporation of liquid anesthetic into the flowing gas stream. The baffle172 is held in place by means of a pressure ring 174 held in place bymeans of the seal 162.

In accordance with a feature of the present invention, the reservoir 144advantageously and conveniently comprises the original container orbottle in which the liquid anesthetic is supplied. As noted above, thisarrangement greatly simplifies handling and use of the anestheticvaporizing unit. The bottle is readily inserted into place on the unit140 by threading the neck of the bottle into an adapter member 176 whichis in turn threaded into an extension 1560 of the base member 156. Thelip of the bottle is sealed by engagement with a sealing block or memberI78 supporting an O-ring 180. It should be understood that variousadapter members 176 may be provided for mating with different types ofbottles containing different anesthetic materials. Thus the vaporizerunit is universally adaptable, and the adapter member I76 serves toprevent the use of an anesthetic material other than the materialintended for use by the operator. In addition, since the chamber 142 andthe reservoir 144 are supported on the base member 156, a unitary,compact and easily handled subassembly is made possible.

As is the case with the liquid anesthetic vaporizer units 10 and 80described previously, evacuation of the liquid anesthetic materialcontained within the reservoir I44 is ac complished by the introductionof pressurized gas into the vaporizer chamber at a level normallybeneath the surface of the liquid. In this manner the rate of flow, andthus the concentration, is maintained independent of the level of liquidcontained within the reservoir. The pressurized gas is introduced intothe reservoir through a conduit I82, while liquid anesthetic material isdischarged from the reservoir vaporized chamber through a liquidcapillary conduit 184. In accordance with a feature of the invention,the conduits I82 and 184 are part of a unitary assembly supported on thebase member 156 and designated as a whole by the reference numeral I86.

More specifically, and referring in particular to FIG. 6, thepressurized gas conduit I82 communicates with a passageway 182a formedwithin the base member I56. The upper end of the conduit I82 is attachedto the base member 156, while its lower end is attached to a fitting 188having an outlet opening into the reservoir 144. The liquid conduit I84extends through a passageway 184a in the base member I56 between thereservoir 144 and the vaporizer chamber 142. Within the reservoir 144,the liquid conduit 182, which is of small, capillary size, is preferablyprotected by a jacket member or tube 190 having its ends connected tothe base member 156 and to the fitting 188. Fluid is admitted to thelower end I84a of liquid conduit 184 through a filter screen 192 held inplace on fitting 188 by a threaded cap I94.

In order to protect the upper portion of the liquid conduit 184 withinthe vaporizer chamber 142, ajacket or tube 196 is provided The lowermostend of jacket I96 is attached to a fitting I98 threaded into the basemember 156 through the porous metal diffusion plate I72v The uppermostend of the jacket I96 supports a drip guide 200 for guiding liquidanesthetic material emerging from the upper end 184!) of the liquidconduit I84 outwardly of the jacket 196 so that it descends onto thediffusion plate 172.

In order to prevent excess pressure buildup within the anestheticreservoir 144 due to evaporation of the liquid anesthetic, there isprovided a bleed passage from the reservoir 144 to the vaporizer 142. Inthe event of a pressure buildup, gas can flow from the reservoir througha small hole 1900 in the jacket I and into the passage 184a in the basemember 156. This gas is then vented into the vaporizer chamber through asmall passage 202 in the fitting 198.

When pressurized gas is admitted to the reservoir I44 through thepassageway 182a and the conduit 182, the reservoir becomes pressurizedand liquid anesthetic material is discharged from the vaporizer throughthe filter screen I92 and the capillary conduit 184 into the vaporizerchamber I42 where it is deposited upon the diffusion plate or baffleI72. A stream of gas to which anesthetic gas is to be mixed enters thevaporizer chamber through the passageway I480 and passes through theporous plate or baffle 172. Liquid anesthetic material reaching thediffusion plate is evaporated into the gas stream, and the anestheticand gas mixture is discharged from the vaporizer chamber 142 through thefitting 162, elbow I66 and conduit I50.

One aspect of the present invention resides in the convenient manner inwhich the base member 156 together with the vaporizer chamber 142 andthe reservoir 144 can be quickly connected to and detached from thehousing I52. Referring now more particularly to FIGS. 4 and 5, thehousing includes a laterally extending support arm 204 defining a recess206 complementary in shape to the projection I56a of the base memberI56. This recess is flanked by a pair ofextensions 204a and 20412 of thearm 204. In order to mount the base member 156 together with thevaporizer chamber 142, the base member 156 is merely dropped into placeon the arm 204.

In order to make connections between the internal pasageways 148a and1820 of the base member 156, each passageway communicates with a quickrelease nipple 208 and 210 respectively. The nipples 208 and 2I0 areslidingly received within recesses 212 and 214 formed in the armextensions 204a and 204i). The recesses 212 and 214 are communicated byway of passageways 218 and 220 (FIG. 6) respectively with the conduitI48 and a pressure line conduit 222 illustrated only in FIG. 3.

In order releasably to interconnect the conduit I50 with the housingI52, the conduit 150 is connected to a slipfit connector 224 engageablewith a nipple 226 (FIG. 5). Consequently, the entire vaporizer assemblycan readily be attached and detached from the housing 152 at will.

Returning to FIG. 3, it can be seen that pressurized gas for supplyingthe pressure line 222 is obtained from a source of pressurized gas byway of the shutoff valve I46. A pressure regulator generally designatedas 228 serves to regulate the pressure within the pressure line 222 andmay if desired be of the construction of the regulator 24 illustrated inmore detail in FIG. I. In addition, flow of pressurized gas through thepressure line 222 is controlled by a shutoff valve generally designatedas 230. In addition, the volume of flow of gas through the conduit 148may be regulated by means of throttling valve generally designated as232.

In accordance with an important feature of the present invention, theshutoff valve 230 in the pressure line 222 and the throttling valve 232in the conduit 148 are combined into a single-valve assembly operable bymeans of a single-manual control. An important advantage of this novelarrangement is that gas is admitted to the vaporizer chamber at the timethe reservoir is pressurized so that the vaporizer cannot be flooded orsubjected to excess liquid anesthetic. More specifically, and asillustrated in FIG. 3, there is provided a single dual-purpose valvegenerally designated as 234 including a central bore 237 defining avalve seat 238 for the shutoff valve 230, In addition, the bore 237receives an adjustable threaded plug 240 defining a seat 242 for thethrottling valve 232.

A valve member 244 is threaded into the opposite end of the bore 237 inorder to control the opening and closing of both valves 230 and 232. Thevalve member 244 includes a first tapered valve surface 244a engageablewith seat 238 and a second tapered valve surface An operating shaft 2440of the valve body member 244 is adapted to be provided with an operatinghandle 246 (FIG. 7) for moving the valve surfaces 244a and 2442: intoand out of engagement with the seals 238 and 242. The plug 240 ispreferably adjusted so that when the valve 230 is fully closed, thevalve 232 is closed as well.

Upon rotation of the handle 246 to open valves 230 and 232, the pressureline shutoff valve 230 opens rapidly to a fully open position due to therelatively abrupt taper of surface 2444. However, due to the relativelygradual taper of surface 244b, the throttling valve 232 opens onlygradually. Consequently, it is possible for the single-operating handle246 to control the dual-purpose valve member for both the shutoff valveand the throttling valve functions.

In accordance with a feature of the invention, the rate of flow ofanesthetic liquid through the liquid conduit 184, and thus theconcentration of the anesthetic mixture provided by the unit 140 iscontrolled by controlling the pressure differential existing betweenopposite ends of the liquid conduit 184. The pressure regulator 228controls the pressure of gas admitted to the reservoir 144 through thepressure line 222. In a similar manner, a back premure regulator 248controls the pressure existing within the conduit 150, and thus thepressure within the vaporizer chamber 142 at the uppermost end of theliquid conduit 184. If desired, the back pressure regulator 248 may besimilar in construction to the regulator 26 illustrated in detail inFIG. 1.

Control of the rate of flow of liquid anesthetic material through theliquid conduit 184 is achieved through adjustment of one or both of thepressure regulators 228 and 248. In the illustrated embodiment of theinvention, the back pressure regulator 248 is normally adjusted by theoperator to vary the flow rate and thus the concentration, while thepressure line regulator 228 is nonnally preadjusted or factory adjustedat a given level. In order conveniently to adjust the rate of flow, anoperating knob 250 for the regulator 248 is positioned in an accessibleposition of the face of the housing 152. The regulator 228 may belocated behind a removable plate 251 on a sidewall of the housing 152(FIG. 7). A differential pressure gauge 252 is connected between thepressure line 222 and the conduit 150 FIG. 3) and gives a pressurereading propor tional to the rate of flow through the liquid conduitI84. Conveniently, this pressure gauge is located on the housing 152above the adjustment knob 250. It should be understood that 244bengageable with seat 242.

if desired a flow indicator could be included in the system, for examplein the conduit 148 or the conduit 150, in accordance with knownpractice.

Convenient attachment of the conduit I48 and the regulator 228 to aconduit 254 (FIG. 3) leading to a source of pressurized gas by way ofthe conventional shutoff valve 146 is made possible by a quick releasetube fitting 256 located on the face of the housing I52 (FIG. 7). Theuse of a single source of gas assures that the vaporizer receives a gasflow whenever the reservoir is pressurized. Connection of the backpressure regulator 248 by way of a conduit 258 to a anesthetic mixtureutilizing apparatus is made possible by another tube fitting 260 on thehousing I52.

The operation of the liquid anesthetic vaporizing unit will be apparentto those skilled in the art from the preceding detailed description.Reviewing the operation, it is assumed initially that the shutoff valve146, the valve 230 and the valve 232 are all in their closed positionsand the unit 140 is not in operation. To prepare the unit for operation,a bottle of a selected liquid anesthetic is attached to the base member156 by means of a mating adapter 176. The vaporizer unit is connected tothe housing 152 of the unit 140 either before of after the bottle ofanesthetic is attached to the base member 156.

In order to begin operation, the shutoff valve I46 is opened to admitpressurized gas to the unit 140 through the fitting 256 on the face ofhousing 152. The operating handle 246 for the valves 230 and 232 is thenopened in order to fully open the shutoff valve 230 and to open thethrottling valve 232 in order that the flow through the conduit 148 isat the desired rate. The back pressure regulator 248 is adjusted througha manipulation of knob 250 until the reading of gauge 252 indicates thatthe desired rate of flow of liquid anesthetic is established.

Pressurized gas then flows from conduit 148 through the vaporizerchamber and by way of conduit 150 through the back pressure regulator248 to the anesthetic mixture utilizing apparatus. Simultaneously,pressure admitted to the reservoir by way of conduit 222 pressurizes thereservoir and forces liquid anesthetic material through the liquidconduit I84 into the reservoir chamber where it is evaporated into thegas stream.

In a liquid anesthetic vaporizing unit similar to the unit 140 andconstructed in accordance with the present invention, it was found thatvarious anesthetic liquids such as ether, halothane, trichloroethyleneand methoxyflurane could be mixed with oxygen at extremely accurate andwidely variable concentration levels. It was found that the rate of flowof the anesthetic material into the vaporizer chamber could beaccurately controlled, independently of the liquid level, by control ofthe pressure drop between the pressure line 222 and the conduit 150 asshown by the reading of the pressure gauge 252. This pressure drop couldreadily be controlled by adjustment of the regulator 248.

For example, it was found that the relationship of anesthetic flow forvarious anesthetic liquids to pressure drop was approximatelyrepresented by the following equations:

In these equations F,, F F, and F, represent the flow of ether,halothane, trichloroethylene and methoxyflurane respectively, expressedin cubic centimeters per minute of the vapor, while 81 represents thepressure drop between the pressure line conduit 222 and the outletconduit 150 expressed in inches of water. Since the flow through theconduit 184 is governed by the rules of laminar flow, the flow is asubstantially linear function of the pressure drop within the operativerange of pressures which may be from about l5 to about 80 or more inchesof water.

lt can thus be seen that the concentration of the anesthetic and gasmixture can be accurately and conveniently controlled through a widerange of concentrations simply by adjustment of the pressure drop andthe rate of gas flow through the vaporizer chamber, For example, ifether is used and the valve 232 is adjusted to permit oxygen to flowthrough the vaporizer chamber 142 at a rate of about 2,000 cubiccentimeters per minute, while the pressure drop is adjusted to about 45inches of water, concentration of about 8 percent of ether in oxygen isobtained. In contrast, if methoxyflurane is used and oxygen is conductedthrough the vaporizer chamber at a rate of about 6,000 cubic centimetersper minute, while the pressure drop is maintained at about inches ofwatena concentration of about 0.34 percent is obtained.

It should be understood that these specific examples are in cluded asillustrative of one particular embodiment of the in vention only, andshould not be taken to limit the scope of the invention.

While the present invention has been described in connection with thedetails of particular embodiments thereof, various other modificationsand embodiments may be devised by those skilled in the art. The presentinvention is not limited to the details of the described embodimentsexcept as included in the appended claims.

What I claim as new and desire to be secured by Letters Patent of theUnited States is:

l. Anesthetic vaporizer for adding anesthetic vapor to a stream of gasin order to provide an anesthetizing gaseous mixture, said vaporizercomprising:

means defining a passageway for the stream of gas;

said passageway defining means including a vaporizer chamber throughwhich the stream of gas flows;

a closed reservoir adapted to be charged with a supply of anesthetic inthe liquid state;

a conduit having one end disposed within said reservoir and havinganother end communicating with said vaporizer chamber, said one endterminating at a point below the normal operating level of the liquid;and

means for pressurizing said reservoir for gradually evacuat ing thesupply of liquid from said reservoir into said vaporizer chamber throughsaid conduit at a rate independent of the level ofliquid in saidreservoir;

said pressurizing means including a pressure line for introducing apressurized gas into said reservoir and communicating with saidreservoir at a region beneath the surface of the liquid anestheticcontained therein.

2. The vaporizer of claim I further comprising adjustable means forcontrolling the pressure differential between said region and theinterior of said vaporizer chamber, thereby to control the rate of flowof liquid through said conduit.

3. The vaporizer of claim 2, said adjustable means comprising a pressureregulator connected to said pressure line for regulating the pressure atsaid region.

4. The vaporizer of claim 2, said adjustable means comprising a pressureregulator communicating with said passageway defining means forregulating the pressure within said vaporizer chamber.

5. The vaporizer of claim 3, said adjustable means further comprising anadditional pressure regulator communicating with said passagewaydefining means for regulating the pressure within said vaporizerchamber.

6. The vaporizer of claim I further comprising a metering valve in saidconduit between said vaporizer and said closed reservoir for varying theresistance to the flow of liquid anesthetic through said conduit.

7. The vaporizer of claim 6 further comprising adjustable means forcontrolling the pressure differential between said region and theinterior of said vaporizer chamber.

8. A liquid anesthetic vaporizing unit for adding anesthetic material toa stream of gas comprising a container adapted to contain a supply ofliquid anesthetic material, a vaporizer including wall means defining anevaporation chamber, a first passage in said wall means for conductingthe stream of gas into said chamber, a second passage in said wall meansfor conducting the stream of gas from said chamber, sealing meanssupported by said wall means, a conduit having a first portion extendingoutwardly from said wall means and having a second portion communicatingwith said chamber for introducing anesthetic material into said chambersaid first portion terminating within said chamber at a point below thenormal operating level of the liquid, means for holding said containeragainst said sealing means with the first portion of said conduitextending into said container, a second conduit ex tending outwardlyfrom said sealing means and received within said container terminatingat a point below the normal operating level of the liquid, and means forintroducing pres surized gas into said second conduit for pressurizingthe region bounded by said container and said sealing means.

9. The unit of claim 8, further comprising means defining a bleedpassageway extending from said container to said chamber for ventingexcess pressures from said container into said chamber.

10. Anesthetic vaporizer for adding anesthetic vapor to a stream of gasin order to provide an anesthetizing gaseous mixture, said vaporizercomprising:

a vaporizer chamber;

inlet and outlet passageways for conducting the stream of gas throughsaid vaporizer chamber;

a reservoir for holding a supply ofliquid anesthetic material;

a conduit extending from said reservoir to said vaporizer chamber forconducting liquid anesthetic to said vaporizer chamber for evaporationinto the stream of gas one end of said conduit terminating below thenormal operating level of the liquid;

a pressure line communicating with said reservoir for pressurizing saidreservoir thereby to force liquid anesthetic to flow through saidconduit one end of said pressure line terminating within said reservoirat a point below the normal operating level ofthe liquid; and

pressure regulating means connected to said outlet passageway forcontrolling the pressure within said vaporizer chamber, thereby tocontrol the rate of flow of liquid anesthetic through said conduit.

11. The anesthetic vaporizer of claim 10 further comprising anadditional pressure regulator connected to said pressure line forcontrolling the pressure within said pressure line.

12. The anesthetic vaporizer of claim ll further comprising a pressureequalizing line extending between said vaporizer chamber and saidadditional pressure regulator for compensating for pressure variationswithin said vaporizer chamber.

[3. A method of producing a mixture of a gas and the vapor ofa liquidanesthetic material from a reservoir comprising the steps of:

passing a stream of gas through a vaporizing chamber communicating withthe reservoir through a conduit which terminates at one end within saidreservoir below the normal operating level of the liquid; and

adding pressurized gas to said reservoir at a point below the surface ofthe liquid anesthetic material contained therein in order to force theliquid anesthetic material through said conduit at a rate of flowsubstantially independent of the liquid level.

14. The method of claim 13 further comprising controlling the pressuredifference between the pressure of said point and the pressure at saidvaporizing chamber in order to meter the flow through said conduit.

15. The method of claim 13 wherein the step of controlling the pressuredifference includes the steps of regulating the pressure of saidpressurized gas, and regulating the pressure of said stream of gas.

16. Apparatus for producing a mixture of anesthetic and gas comprising areservoir for a supply of anesthetic in liquid form, a vaporizerchamber, first conduit means for passing a stream of gas through saidchamber, a liquid passageway for discharging liquid anesthetic from saidreservoir into said chamber for evaporation into said stream of gen oneend of said passageway terminating at a point below the normal 17. Theapparatus of claim 16, said valve assembly including a valve bore, firstand second seats in said bore, and a single valve member movable in saidbore having first and second valve seating surfaces engageable with saidfirst and second seats to close said first and second valves.

18. The apparatus of claim 17, said first and second valve seatingsurfaces being constructed and arranged with respect to said first andsecond seats so that said first valve is a shutoff valve and said secondvalve is a throttling valve

1. Anesthetic vaporizer for adding anesthetic vapor to a stream of gas in order to provide an anesthetizing gaseous mixture, said vaporizer comprising: means defining a passageway for the stream of gas; said passageway defining means including a vaporizer chamber through which the stream of gas flows; a closed reservoir adapted to be charged with a supply of anesthetic in the liquid state; a conduit having one end disposed within said reservoir and having another end communicating with said vaporizer chamber, said one end terminating at a point below the normal operating level of the liquid; and means for pressurizing said reservoir for gradually evacuating the supply of liquid from said reservoir into said vaporizer chamber through said conduit at a rate independent of the level of liquid in said reservoir; said pressurizing means including a pressure line for introducing a pressurized gas into said reservoir and communicating with said reservoir at a region beneath the surface of the liquid anesthetic contained therein.
 2. The vaporizer of claim 1 further comprising adjustable means for controlling the pressure differential between said region and the interior of said vaporizer chamber, thereby to control the rate of flow of liquid through said conduit.
 3. The vaporizer of claim 2, said adjustable means comprising a pressure regulator connected to said pressure line for regulating the pressure at said region.
 4. The vaporizer of claim 2, said adjustable means comprising a pressure regulator communicating with said passageway defining means for regulating the pressure within said vaporizer chamber.
 5. The vaporizer of claim 3, said adjustable means further comprising an additional pressure regulator communicating with said passageway defining means for regulating the pressure within said vaporizer chamber.
 6. The vaporizer of claim 1 further comprising a metering valve in said conduit between said vaporizer and said closed reservoir for varying the resistance to the flow of liquid anesthetic through said conduit.
 7. The vaporizer of claim 6 further comprising adjustable means for controlling the pressure differential between said region and the interior of said vaporizer chamber.
 8. A liquid anesthetic vaporizing unit for adding anesthetic mateRial to a stream of gas comprising a container adapted to contain a supply of liquid anesthetic material, a vaporizer including wall means defining an evaporation chamber, a first passage in said wall means for conducting the stream of gas into said chamber, a second passage in said wall means for conducting the stream of gas from said chamber, sealing means supported by said wall means, a conduit having a first portion extending outwardly from said wall means and having a second portion communicating with said chamber for introducing anesthetic material into said chamber said first portion terminating within said chamber at a point below the normal operating level of the liquid, means for holding said container against said sealing means with the first portion of said conduit extending into said container, a second conduit extending outwardly from said sealing means and received within said container terminating at a point below the normal operating level of the liquid, and means for introducing pressurized gas into said second conduit for pressurizing the region bounded by said container and said sealing means.
 9. The unit of claim 8, further comprising means defining a bleed passageway extending from said container to said chamber for venting excess pressures from said container into said chamber.
 10. Anesthetic vaporizer for adding anesthetic vapor to a stream of gas in order to provide an anesthetizing gaseous mixture, said vaporizer comprising: a vaporizer chamber; inlet and outlet passageways for conducting the stream of gas through said vaporizer chamber; a reservoir for holding a supply of liquid anesthetic material; a conduit extending from said reservoir to said vaporizer chamber for conducting liquid anesthetic to said vaporizer chamber for evaporation into the stream of gas one end of said conduit terminating below the normal operating level of the liquid; a pressure line communicating with said reservoir for pressurizing said reservoir thereby to force liquid anesthetic to flow through said conduit one end of said pressure line terminating within said reservoir at a point below the normal operating level of the liquid; and pressure regulating means connected to said outlet passageway for controlling the pressure within said vaporizer chamber, thereby to control the rate of flow of liquid anesthetic through said conduit.
 11. The anesthetic vaporizer of claim 10 further comprising an additional pressure regulator connected to said pressure line for controlling the pressure within said pressure line.
 12. The anesthetic vaporizer of claim 11 further comprising a pressure equalizing line extending between said vaporizer chamber and said additional pressure regulator for compensating for pressure variations within said vaporizer chamber.
 13. A method of producing a mixture of a gas and the vapor of a liquid anesthetic material from a reservoir comprising the steps of: passing a stream of gas through a vaporizing chamber communicating with the reservoir through a conduit which terminates at one end within said reservoir below the normal operating level of the liquid; and adding pressurized gas to said reservoir at a point below the surface of the liquid anesthetic material contained therein in order to force the liquid anesthetic material through said conduit at a rate of flow substantially independent of the liquid level.
 14. The method of claim 13 further comprising controlling the pressure difference between the pressure of said point and the pressure at said vaporizing chamber in order to meter the flow through said conduit.
 15. The method of claim 13 wherein the step of controlling the pressure difference includes the steps of regulating the pressure of said pressurized gas, and regulating the pressure of said stream of gas.
 16. Apparatus for producing a mixture of anesthetic and gas comprising a reservoir for a supply of anesthetic in liquid form, a vaporizer chamber, first conduit means for passinG a stream of gas through said chamber, a liquid passageway for discharging liquid anesthetic from said reservoir into said chamber for evaporation into said stream of gas one end of said passageway terminating at a point below the normal operating level of the liquid, second conduit means for passing a stream of pressurized gas into said reservoir for forcing said liquid anesthetic into said liquid passage one end of said second conduit means terminating at a point below the normal operating level of the liquid, and a control valve assembly for controlling flow through said first and second conduits means, said control valve assembly comprising a first valve in said first conduit means, a second valve in said second conduit means, and a single manually operated means for simultaneously opening both said first and second valves.
 17. The apparatus of claim 16, said valve assembly including a valve bore, first and second seats in said bore, and a single valve member movable in said bore having first and second valve seating surfaces engageable with said first and second seats to close said first and second valves.
 18. The apparatus of claim 17, said first and second valve seating surfaces being constructed and arranged with respect to said first and second seats so that said first valve is a shutoff valve and said second valve is a throttling valve. 